I have a box with holes in it. I have one light inside that provides a great sss effect to the walls of the box but I need light rays bursting out of the holes so I have chosen to use a separate light for that which is driven by a low res copy of the box with holes - otherwise the sss would be blown out. Is it possible to exclude the SSS texture from seeing that low res copy of the box?
assuming standard render (or physical I guess)... why do you need two lights? But assuming you do, I don't think you don't need a low poly box for the second light that has visible volumetric, just check No Illumination in the Visible Volumetric light - it can still produce visible light without adding light to the SSS (or the rest of the scene)